RE: [lwip-users] TCP Checksum errors.

[Nick Thomas]

> -----Original Message-----
> From: address@hidden
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> You said before that UDP and DHCP (which is UDP) are running fine... Do
> you use the raw API? If so, UDP packets will get send in one piece (i.e.
> your netif driver will see them as one pbuf with p->len == p->tot_len
> and p->next == NULL). However, when sending TCP packets, the stack may
> chain multiple pbufs for one packet in which case the driver has to copy
> the data of multiple pbufs before sending a packet. There may be
> something wrong in the driver here! (especially since your other HW
> platform might use a different netif driver?)

Hi, I am using the netconn_X functions. In stepping through
inet_chksum_pseudo() routine I notice that checksum errors are observed when
there is more than one pbuf in the chain. I never seem to get more than 2
pbufs in a chain. But, anyway, when the chain only has one pbuf then the
checksum appears to be calculated OK (at least wireshark doesn't complain
about it.).

Still more debugging to do, but getting nearer.

Thanks for the advice.

Regards

Nick


>
> However, if you used UDP with the netif or sockets API, this won't be
> the problem as UDP packets are always a chain of 2 pbufs here (one
> PBUF_RAM for headers and one PBUF_REF for data).
>
> I don't think your ethernet HW has checksum capabilities or even turned
> them on - if so, the checksums would be OK ;-)
>
> Simon
>
>
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